1. Technical Field
The present invention generally relates to pneumatic tires and devices for monitoring the conditions of the tires. More particularly, the present invention is related to a radio frequency active monitor assembly that is housed in a protective body that is placed in a tire and is free to move about while the tire is in use with nothing connecting the monitor assembly to the tire or tire rim. Specifically, the present invention relates to a monitoring device for a pneumatic tire that is housed in a substantially spherical protective body. The spherical body is placed loosely between a tire and a tire rim when the tire is mounted on the tire rim and allowed to freely move about the inside of the tire.
2. Background Information
It is often desired in the art to monitor the conditions of tires while they are installed and in use on a particular vehicle. It is particularly desirable to measure the internal temperature and internal pressure of a tire. These measurements are preferably capable of being taken while the tire is in use without having to remove the tire from the vehicle or otherwise interrupt the use of the vehicle to take the measurements. It is particularly desirable to monitor the conditions and statistics of large off-the-road truck tires because the off-the-road tires are expensive and subject to harsher conditions that typical passenger car tires. The off-the-road tires on large trucks and other vehicles must be regularly maintained to maximize vehicle and tire efficiency.
Numerous types of monitoring devices are known in the art. One type of known monitoring device uses a passive integrative circuit embedded within the body of the tire that is activated by a radio frequency transmission that energizes the circuit by inductive magnetic coupling. Other prior art devices used for monitoring tire conditions include self-powered circuits that are positioned external of the tire, such as at the valve stem. Other active, self-powered programmable electronic devices are disclosed in U.S. Pat. Nos. 5,500,065, 5,573,610, 5,562,787, and 5,573,611 which are assigned to the Assignee of the present application.
One problem common to each of these monitoring devices is the problem of attaching the monitoring device to the tire with a stable and lasting attachment. The attachment problem is difficult when the monitoring device is attached to the inside of the tire, the outside of the tire, or embedded within the body of the tire. Each of these locations creates different problems with the attachment process as well as the manufacturing process of the tire. It is generally undesirable to provide an attachment configuration that requires re-tooling or any re-directing of the existing tire manufacturing lines. It is thus desired in the art to provide a monitoring device for a pneumatic tire that obviates the attachment problems inherent with the prior art monitoring devices.
The prior art attachment problems exist because the forces on an electronic monitoring device while connected to a pneumatic tire are significant and numerous. Tires not only are subjected to rotational forces when the vehicle is moving but are also subjected to various impact forces when the tire contacts bumps or surface irregularities. The attachment of the monitoring device to the tire must be strong enough and secure enough to maintain the position of the monitoring device with respect to the tire while experiencing all of these forces while also protecting the monitoring device from damage resulting from these forces. These concerns have lead to the encapsulation of the monitoring devices and numerous methods of attaching the monitoring device to the internal wall of a tire.
The attachment of the monitoring device to the internal wall of the tire requires the tire to be balanced about its rotational axis prior to use. The monitoring device itself adds weight to the tire and the attachments known in the art add further weight to the tire requiring the tire to be counterbalanced. It is thus desired to provide a monitoring device that may be used with a tire without requiring the tire to be counterbalanced.
Another significant problem experienced with attaching a monitoring device to a pneumatic tire is that the surface of the tire where the monitoring device is typically anchored is not stable. Tires are designed to flex and stretch to accommodate various pressures and forces. The attachment of the monitoring device to the tire must accommodate the movement and stretching of the tire surface where the monitoring device is connected. Such accommodation must last throughout the life of the tire and function at a wide range of temperatures and pressures. It is thus desired in the art to provide a monitoring device that may be used with a pneumatic tire without being connected to one of the tire surfaces that flexes and stretches.